1. Field of the Invention
The invention pertains to the field of isolation of vibrations in rotating systems. More particularly, the invention pertains to a balance shaft with a torsion bar.
2. Description of Related Art
The engine arrangement of cylinders and the number of cylinders influence the balance of the engine and the vibration the engine produces. Certain popular engine configurations, such as four cylinder inline engines, are kinematically unbalanced. This results in excessive levels of vibration, which often times are found to be objectionable to the end customer. Balance shafts cancel or reduce some of the vibration produced by the engine.
Prior art FIG. 1 shows a torsion bar 4 fixedly attached to a sprocket 2 in which a chain 1 is wrapped, on a first end. The second end of the torsion bar 4 is attached to the balance shaft 8. The torsion bar 4 has at least two pairs 6a, 6b of bearings on either end to maintain the position of the torsion bar 4 relative to the balance shaft 8. The balance shaft 8 contains a weight 10 on a portion of the shaft.
An example of a balance shaft used to reduce the vibration of the engine is U.S. Pat. No. 5,253,547 which discloses a balance shaft installed into an in-line engine that includes a first journal and a second journal with first and second bearings that support the shaft. The first bearing is near the front side of the engine through a retainer. The second bearing is near a generally center portion in the axial direction of the crankshaft and secured to the cylinder block. The balance shaft also includes an oil passage, which is formed along the center axis of the shaft and communicates with grooves that splash the oil onto the outer circumferential surface of the balance shaft. The splashed oil lands on the first and second journal.
JP 07-238971A discloses a torsion spring in a damper shaft, which is inserted into a tubular casing. The casing is then attached to an equipment body.
Another examples is JP 04-228950A, which discloses a balance shaft comprising an elastic rod member with spring properties that acts as torsion bar against vibration of the crankshaft. A second shaft is connected to the crankshaft via a damper member, which is positioned in parallel to the balance shaft. The damper member follows the rotation of the crankshaft. When a difference occurs between the rotation of the second shaft and another rotation due to engine output transmission through the balance shaft, a damping force is generated.
JP 06-191461A discloses torsion bars for motorcycles that act as springs and are attached to the sides of swing arm. At least one of the torsion bars is disposed within the hollow, rotating shaft of the rotary damper. When the torsion bars act as springs, the spring forces act on the right and left swing arms.